1. Field of the Invention
The present invention relates to a liquid crystal display, and more particularly, to a liquid crystal display and a method for fabricating the same, which has large aperture and can improve a poor picture quality caused by vertical cross talk.
2. Background of the Related Art
A related art liquid crystal display is provided with a liquid crystal panel, a light source, and a driving circuit. The liquid crystal panel has first and second substrates, and liquid crystal injected between the two substrates. The second substrate has a black matrix, a color filter layer, and a common electrode.
The first substrate has a plurality of gate lines running in one direction at fixed intervals, a plurality of data lines running in one direction perpendicular to the gate lines at fixed intervals, and an LCD array at crossing parts of the gate lines and the data lines.
In an LCD array region, a space region between the gate lines and data lines is a pixel region, in which a pixel electrode and a thin film transistor are provided. That is, the thin film transistor is provided with a gate electrode connected to the gate line, a source electrode connected to the data line, a data electrode connected to the pixel electrode, for being turned on selectively in response to a signal to the gate line to transfer a data signal from the data line to the pixel electrode. The gate lines and the data lines are electrically connected to driving circuits.
Vertical cross-talk in the liquid crystal display, caused by parasitic capacitance Cds between the source electrode and the drain electrode, degrades a picture quality as a source voltage (a data signal) to be provided to the pixels on a vertical (data) line influences the liquid crystal pixel voltage. The cross-talk mostly occurs as a static capacitance between the data line and the pixel electrode is increased. Research has been performed with a goal to reduce the vertical cross-talk in a liquid crystal display with a large aperture. In order to achieve the large aperture, an organic insulating film is used as a passivation film deposited between the data line and the pixel electrode, and the pixel electrode is overlapped with and edge of the data line.
A related art liquid crystal display and method for fabricating the same will be explained, with reference to the attached drawings. FIG. 1 illustrates a layout of a first substrate of the related art liquid crystal display, and FIG. 2 illustrates a section of the related art liquid crystal display across line I–I′ in FIG. 1, showing a pixel electrode, a data line, and a drain electrode.
Referring to FIGS. 1 and 2, the related art liquid crystal display is provided with an active layer 102, a channel layer of a thin film transistor in an active region defined on an insulating substrate 101, a gate insulating film (not shown) on the active layer 102 to surround the active layer 102, and a gate electrode 103a crossing a central part of the active layer 102 on the gate insulating film. The gate electrode 103a is a projection from the gate line 103 running in one direction. There are source/drain regions in the active layer on both sides of the gate electrode 103a, an interlayer insulating film 104 on an entire surface inclusive of the gate electrode 103a, and first contact holes 106 to expose the source/drain regions in the active layer 102 by etching the interlayer insulating film 104 and the gate insulating film. The source electrode 105a, the drain electrode 105b, and the data line 105 are formed at each of the contact holes 106 and on the interlayer insulating film 104. The data line 105 and the gate line 103 cross each other. An organic insulating film 107 is formed on the interlayer insulating film 104 inclusive of the source electrode 105a, the drain electrode 105b, and the dateline 105. The organic insulating film 107 has a flat surface. There is a second contact hole 108 in the organic insulating film 107 to expose the drain electrode 105b, and a pixel electrode 109 of ITO (Indium Thin Oxide) in the second contact hole 108 and on the organic insulating film 107. The pixel electrode 109 overlaps upper parts of edges of the data line 105, except the central part thereof.
Referring to FIG. 2, in a large aperture structure, a distance ‘b’ between the pixel electrode 109 and the data line 105 is the most important element in view of the vertical crosstalk. That is, the greater the distance ‘b’, the smaller the parasitic capacitance between the pixel electrode 109 and the data line 105, that improves the poor picture quality caused by the vertical crosstalk. However, the distance ‘b’ can not be made greater because an increased distance ‘b’ necessitates an increase of an etch depth ‘c’ of the second contact hole 108 provided for bringing the pixel electrode 109 into contact with the drain electrode 105. In conclusion, ‘c’ is fixed depending on a dry etching (anisotropic etching) capability, ‘a’ is fixed depending on ‘c’, and ‘b’ is fixed depending on ‘c’. For an example, when ‘c’=9500 Å, ‘d’=3500 Å, ‘a’=1.3 μm, and ‘b’=0.95 μm. If ‘b’ is to be made thicker, then ‘c’ also has to be made thicker.
A method for fabricating the foregoing related art liquid crystal display will be explained. FIGS. 3A˜3C illustrate sections showing the steps of a method for fabricating the related art liquid crystal display.
Referring to FIG. 3A, an active layer 102 (see FIG. 1) is formed on an active region defined on an insulating substrate 101, a gate insulating film (not shown) is formed on the active layer 102 to surround the active layer 102, and a gate line 103 (see FIG. 1) is formed on the gate insulating film to run in one direction, together with a gate electrode 103a (see FIG. 1) projected from the gate line 103 to cross a central part of the active layer 102. Source/drain regions are formed in the active layer on both sides of the gate electrode 103a. 
Then, as shown in FIG. 3B, an interlayer insulating film 104 is deposited on an entire surface inclusive of the gate electrode 103a, and the interlayer insulating film 104 and the gate insulating film are etched to expose the source/drain regions in the active layer 102, to form a first contact hole 106 (see FIG. 1). A metal layer is formed in respective first contact holes 106 to the source and drain regions and on the interlayer insulating film 104, and subjected to anisotropic etching, to form a source electrode 105a (see FIG. 1) in contact with the source region, a drain electrode 105b in contact with the drain region, and a data line 105 extended from the source electrode to be in a perpendicular direction to the gate line 103.
As shown in FIG. 3C, an organic insulating film 107 is coated on an entire surface of the source electrode 105a, the data line 105, and the drain electrode 105b, and a second contact hole 108 is formed on the organic insulating film 107 to expose the drain electrode 105b. An ITO (Indium Tin Oxide) is deposited on an entire surface of the organic insulating film 107 inclusive of the second contact hole 108, and subjected to anisotropic etching to expose a central part of the data line 105, and overlaps upper part edges of the data line 105, to form a pixel electrode 109.
However, the foregoing related art liquid crystal display, and a method for fabricating the same, have the following problem.
The thicker organic insulating film formed between the data line and the pixel electrode for reduction of a parasitic capacitance between the data line and the pixel electrode requires a longer time period in etching a second contact hole to bring the drain electrode and the pixel electrode into contact. Accordingly, the related art has a limitation in providing a liquid crystal display, which reduces a vertical crosstalk while a large aperture is achieved, for improving a picture quality.